The present invention generally relates to a method and an apparatus for loading/unloading a wafer cassette onto/from a loadport of a process machine and more particularly, relates to a method and an apparatus for loading a wafer cassette that is equipped with a position verification finger onto a loadport of a process machine that is equipped with a position verification block such that the misplacement of a wafer cassette onto a process machine can be avoided.
In the manufacturing of a semiconductor device, the device is usually processed at many work stations or processing machines. The transporting or conveying of partially finished devices, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles (AGV) or overhead transport (OHT) vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle.
An OHT system is frequently used to deliver a cassette pod such as a FOUP to a process machine. This is shown in FIG. 1. A cassette pod 10 of the FOUP type is positioned on a loadport 12 of a process machine 14. The loadport 12 is frequently equipped with a plurality of locating pins 16 for the proper positioning of the cassette pod 10. A detailed perspective view of the FOUP 10 is shown in FIG. 2. The FOUP 10 is constructed of a body portion 18 and a cover portion 28. The body portion 18 is provided with a cavity 46 equipped with a multiplicity of partitions 48 for the positioning of 25 wafers of the 300 mm size. The body portion 18 is further provided with sloped handles 50 on both sides of the body for ease of manual transportation. On top of the body portion 18, is provided with a plate member 52 for gripping by a transport arm (not shown) of an OHT system (not shown).
During wafer processing, the wrong wafer cassette pod is sometimes placed on a loadport of a process machine. The machine-readable tag positioned on the side of the cassette pod and the tag reader mounted on the conveying vehicle do not always prevent such error from occurring. When the misplacement of a cassette pod on a process machine occurs, for instance, when a cassette pod filled with wafers to be processed in a front-end-of-line process is placed on a process machine that executes a back-end-of-line process, serious contamination problem occurs both on the wafers and in the process chamber. Similarly, serious contamination on the wafers and in the process chamber occurs when a cassette pod filled with wafers for a cobalt process is placed on a process machine that is used for depositing copper layers. It is desirable to have a method that can automatically detect such error when not detected by a human operator or by a tag reader.
It is therefore an object of the present invention to provide a contamination prevention device on a cassette pod for loading onto a process machine that does not have the drawbacks or shortcomings of conventional cassette pods.
It is another object of the present invention to provide a method for preventing misplacement of a cassette pod onto a process machine so that serious contamination to the wafers and to the process chamber can be avoided.
It is a further object of the present invention to provide a method for preventing misplacement of a cassette pod onto a process machine by mounting position verification fingers on the cassette pod and a position verification block on the process machine.
It is another further object of the present invention to provide a method for preventing misplacement of a cassette pod on a process machine by mounting position verification fingers on the cassette pod corresponding to the position of a position verification block mounted on the process machine onto which the cassette pod is to be placed.
It is still another object of the present invention to provide an apparatus for preventing misplacement of a cassette pod onto a process machine which includes a cassette pod, a process machine, at least one position verification block mounted on the process machine, and at least one position verification finger mounted on the cassette pod.
It is yet another object of the present invention to provide an apparatus for preventing misplacement of a cassette pod onto a process machine by providing various pairs of matched-position verification block/verification finger for various fabrication processes to be conducted on the process machine.
In accordance with the present invention, a method and an apparatus for preventing the misplacement of a cassette pod onto a process machine and thus avoiding contamination problems are provided.
In a preferred embodiment, a method for preventing misplacement of a cassette pod onto a process machine can be carried out by the operating steps of first providing a cassette pod that has a front panel, a back panel and two side panels; providing a process machine that is equipped with a loadport for receiving the cassette pod thereon; mounting at least one position verification block immediately adjacent to an outside periphery of the loadport at a first preset position on the process machine; and mounting at least one position verification finger on the front panel of the cassette pod at a first preset position on the front panel corresponding to the first preset position of the at least one position verification block such that when the cassette pod is mounted on the loadport, the at least one position verification finger does not interfere with and has a clearance of at least 1 mm from the at least one position verification block.
The method for preventing misplacement of a cassette pod on a process machine may further include the step of mounting two position verification blocks adjacent to the outside periphery of the loadport which are at least 5 cm apart from each other, the step of mounting one position verification finger on the front panel of the cassette pod, the step of adhesively mounting the at least one position verification block on the process machine, or the step of mechanically mounting the at least one position verification block on the process machine.
The method may further include the step of mounting a first position verification block at a first preset position on the process machine when the process machine is used for a front-end-of-line (FEOL) process, and mounting a second position verification block at a second preset position on the process machine when the process machine is used for a back-end-of-line (BEOL) process.
The method may further include the step of mounting a third position verification block at a third preset position on the process machine when the machine is used for a cobalt deposition process, and mounting a fourth position verification block at a fourth preset position on the process machine when the process machine is used for a copper deposition process.
The method may further include the step of mounting a first position verification finger at a first preset position on the front panel of the cassette pod when the pod is used for holding wafers for a FEOL process, or the step of mounting a second position verification finger at a second preset position on the front panel of the cassette pod when the cassette pod is used for holding wafers for a BEOL process. The method may further include the step of mounting a third position verification finger at a third preset position on the front panel of the cassette pod when the pod is used for holding wafers for a cobalt deposition process, or the step of mounting a fourth position verification finger at a fourth preset position on the front panel of the cassette pod when the pod is used for holding wafers for a copper deposition process.
The present invention is further directed to an apparatus for preventing misplacement of a cassette pod on a process machine which includes a cassette pod that has a front panel, a back panel and two side panels; a process machine that is equipped with a loadport for receiving the cassette pod thereon; at least one position verification block mounted immediately adjacent to an outside periphery of the loadport at a first preset position on the process machine; and at least one position verification finger on the front panel of the cassette pod at a first preset position on the front panel corresponding to the first preset position of the at least one position verification block such that when the cassette pod is mounted on the loadport, the at least one position verification finger does not interfere with and has a clearance of at least 1 mm from the at least one position verification block.
In the apparatus for preventing misplacement of a cassette pod on a process machine, the at least one position verification block may be two position verification blocks mounted on the process machine, the at least one position verification finger may be one position verification finger mounted on the front panel of the cassette pod. The at least one position verification block may be mounted on the process machine by adhesive means, or by screw means. The at least one position verification block may include a first position verification block mounted at a first preset position on the process machine used in a FEOL process. The at least one position verification block may include a second position verification block mounted at a second preset position on the process machine used in a BEOL process. The at least one position verification finger may include a first position verification finger mounted at a first preset position on the front panel of the cassette pod which holds wafers for a FEOL process, or may include a second position verification finger mounted at a second preset position on the front panel of the cassette pod which holds wafers for a BEOL process.